1. Field of the Invention
The present invention relates to a fluid coupling device to lead a fluid into a rotary shaft rotated at high speed.
2. Description of Related Art
One type of conventional fluid coupling device is shown in FIG. 4. This fluid coupling device is a contact type fluid coupling device which uses a contact type mechanical sealing system. In a coupling main body 101 having a generally cylindrical shape, bearings 102 are provided. A coupling shaft 103 is rotatably supported by the bearings 102. The left end of the coupling shaft 103 is coaxially fixed to a rotatable main shaft (not shown) of a machine tool. Therefore, the coupling shaft 103 is rotatable together with the main shaft. In the coupling shaft 103, an axial fluid passage 104 is formed. The fluid passage 104 is opened at the right end surface of the coupling shaft 103.
A rear body 100 is fixed at the right end surface of the coupling main body 101. A fluid supply port 105 is formed in the rear body 100. In the coupling main body 101, a seat ring 107 is provided slidable in an axial direction of the coupling main body 101 and coupling shaft 103. The rotation of the seat ring 107 is restricted by a pin 108. A fluid passage 106 which communicates with the fluid supply port 105, of the rear body 100, is formed in the center of the seat ring 107. A spring 109 is provided between the seat ring 107 and the rear body 100. The seat ring 107 is urged toward the left direction, in FIG. 4, by the spring 109.
A follower ring 110 is fixedly coupled to the right end surface of the coupling shaft 103. The left end surface of the seat ring 107 is urged to be pressed toward the right end surface of the follower ring 110 by the spring 109. When a coolant is supplied from the fluid supply port 105 to the fluid passage 104, of the coupling shaft 103 which is rotated with the main shaft of the machine tool, through the fluid passage 106, the follower ring 110 is hermetically and slidingly rotated relative to the end surface of the seat ring 107. The fluid passages 104 and 106 are, therefore, hermetically sealed.
Another type of conventional fluid coupling device is disclosed in Japanese Utility Model Laid-Open Publication No.1-84941. This device is a non-contact type fluid coupling device as shown in FIG. 5. A main shaft 119 is rotatably supported to a frame 121 of a machine tool. An axial fluid passage 120 is formed in the main shaft 119. Bearings 116 are provided in a coupling main body 111, fixed to the frame 121 of the machine tool. A coupling shaft 113 is rotatably supported by the bearings 116. An axial fluid passage 118 is formed in the coupling shaft 113. The left end surface of the coupling shaft 113 is fixed to the main shaft 119. Therefore, the coupling shaft 113 is rotated together with the main shaft 119. Moreover, the fluid passage 118 of the coupling shaft 113 communicates with the fluid passage 120 of the main shaft 119. A rear body 112 is engaged and fixed to the right end surface of the coupling main body 111. A fluid supply port 117, to which the coolant or the fluid is supplied, and a fluid passage 115, which communicates with the fluid passage 118 of the coupling shaft 113, are formed in the rear body 112. A minute space 114 is formed between the right end surface of the coupling shaft 113 and the left end surface of the rear body 112, so that a non-contact condition is maintained between the coupling shaft 113 and the rear body 112. Therefore, the coolant in the fluid passages 118 and 115 is sealed by the minute space 114 when the coolant is supplied from the fluid supply port 117 to the fluid passage 118, of the coupling shaft 113, through the fluid passage 115 in order to supply the coolant to the fluid passage 120 of the main shaft 119 of the machine tool. Any coolant which leaks from the minute space 114 is discharged outside through drain holes 122 and 123 formed in the coupling main body 111.
With the above first described conventional arrangement, where the fluid coupling device is maintained by the contact type mechanical sealing system, in which the follower ring 110 is in facial sliding contact with the end surface of the seat ring 107, the rotational speed of the coupling shaft 103 should be at a relatively low level, otherwise frictional wear may occur at the interfaces of the follower ring 110 and the seat ring 107.
Moreover, if the applied coolant has a high pressure, a high sealing performance at the interface, to prevent the coolant from leaking between the follower ring 110 and the seat ring 107, is required. To achieve this, the biasing force of the spring 109 must be increased. Accordingly, the rotational speed of the coupling shaft 103 must be further lowered to avoid frictional wear.
In summary, the contact type fluid coupling device is therefore not available for high speed rotation of the coupling shaft 103. Further, the contact type fluid coupling device cannot perform idle rotation of the coupling shaft 103 without supplying coolant to protect the sliding surfaces of the follower ring 110 and the seat ring 107. Lastly, a filter unit is required to prevent entry of high hardness particles into the fluid passage when supplying the coolant, otherwise the high hardness particles may damage the sliding surface of the follower ring 110 and the seat ring 107.
On the other hand, the conventional non-contact type fluid coupling device is better for high speed rotation than is the contact type fluid coupling device. However, if the applied fluid has high pressure, fluid leakage may occur so that the coolant leaked from the minute space 114 may enter the bearings 116 to thereby degrade their inherent rotation function. Specially, aqueous coolant or pure water cannot be employed as the coolant passing through the fluid passage 118 since leakage of such a coolant from the minute space 114 may lead to corrosion of the bearings 116.
Further, in the conventional contact type fluid coupling device, the coupling shaft 103 is supported by the bearings 102; and in the conventional non-contact type fluid coupling device, the coupling shaft 113 is supported by the bearings 116. When the coupling shafts 103 or 113 are rotated, the bearings 102 or 116 generate both heat and vibration. The generated heat and the vibration both affect the apparatus on which the fluid coupling device is provided, for example, the machine tool. Moreover, the rotational speed of the coupling shafts 103 or 113 depend on the efficiency of the bearings 102 or 116. In other words, the rotational speed of the rotation shaft to which the fluid is supplied through the fluid coupling device, for example, the main shaft of the machine tool, is limited in accordance with the efficiency of the bearings 102 or 116 of the fluid coupling device.